The present invention relates to liquid jet heads, liquid jet apparatuses, and methods for manufacturing the liquid jet head. The present invention is particularly applied to a liquid jet apparatus using a thermal head to ensure satisfactory reliability even if a wiring pattern is formed of a wiring material having an enhanced electromigration resistance.
Needs for color hard copies have recently been growing in the field of image processing and the like. According to the needs, methods for making color hard copies are proposed which include a sublimation dye transfer method, a thermofusible transfer method, liquid jet methods such as ink jetting, electrophotography, and a silver salt photothermographic method.
In the liquid jet methods from among those methods, droplets of, for example, a recording liquid (ink) are discharged to form dots from nozzles provided to a recording head onto a recording object. Thus, high-quality images can be output from a simple structure. The liquid jet methods are classified into, for example, the electrostatic attraction system, the continuous vibration generating system (piezo system), and the thermal system by how to discharge liquid such as ink.
In the thermal system, liquid, such as ink, is locally heated to generate bubbles that push the liquid to discharge onto a printing object. Thus, high quality color images can be printed out from a simple structure.
A printer using the thermal system includes a so-called printer head. The printer head includes a semiconductor substrate provided thereon with heating elements for heating a liquid such as ink, a driving circuit using a logic integrated circuit for driving the heating elements, and the like by semiconductor technology.
Specifically, the thermal head has a logic integrated circuit constituted of MOS transistors or bipolar transistors; and driving transistors driven by the logic integrated circuit, on a silicon substrate. Also, Ta, Ta2N, TaAl, or the like is deposited to form a thin film serving as the heating elements, by sputtering. Then, a wiring material, such as aluminium, is deposited and patterned by wet etching to connect the transistors with the respective heating elements. Furthermore, a protective layer, such as a silicon nitride film, and an anti-cavitation layer using a Ta film are formed. The thermal head also includes liquid chambers for holding a liquid such as ink and channels for drawing the liquid to the respective liquid chambers. Thus, the logic driving circuit controls the driving transistors to excite the heating elements, and, thereby, the thermal head discharges ink droplets from the nozzles.
In order to produce a printed output with a high resolution, it is desired that the heating elements are densely arranged in the thermal head. For example, in a printer head having a resolution corresponding to 600 DPI, heating resistors are aligned at intervals of 42.333 μm.
When the driving transistors are connected to the respective heating elements with pure aluminium serving as a wiring material, wet etching with a chemical solution mainly containing phosphoric acid or the like facilitates reliable patterning of the aluminium, without negatively affecting the heating elements.
However, if current is applied to the aluminium, electrons come into collision with aluminium atoms, thereby moving the aluminium atoms. As a result, a deficiency may occur in part of the aluminium wiring pattern. Also, the deficiency may result in a break in the wiring pattern (so-called electromigration deficiency). In the process of preparing semiconductors, accordingly, silicon, copper, or the like is added to aluminium, instead of using pure aluminium, so that aluminium grain boundaries are reinforced with such an additive, thereby enhancing the electromigration resistance.
It is, therefore, considered that the reliability of the thermal head can further be increased by use of a wiring material having an enhanced electromigration resistance. In this instance, therefore, it is considered that electromigration resistance can be enhanced by, for example, forming heating elements 2 and a wiring layer 3 of a wiring material, such as Al—Si or Al—Cu, in that order on a semiconductor substrate 1 including driving transistors, after forming an insulating layer on the semiconductor substrate 1, and by patterning the wiring layer by wet etching, as shown in FIG. 1.
Unfortunately, the additive in the wiring material, such as Si or Cu, does not dissolve in an etching chemical, and, therefore, residues 4 constituted of Si, Cu, or the like remain in the region where the wiring material has been removed by the chemical. In the case of use in the thermal head, this region, where the wiring material has been removed, acts as a source of dust that seriously, adversely affects semiconductor preparing processes.
As one of the solution of this problem, halogen gas plasma (that is, dry etching) may be substituted for wet etching to form an Al—Si or Al—Cu wiring pattern. In this dry etching using a halogen gas, however, the material of the heating elements, such as Ta, Ta2N, or TaAl, is undesirably etched, and, consequently, the reliability of the heating elements is seriously degraded.
Thus, it has been difficult to ensure the reliability of the thermal head by use of a wiring material having an enhanced electromigration resistance.